1. Field of the Invention
The present invention relates to a semiconductor device and a method of fabricating the same, and more particularly to a metal interconnection structure of a semiconductor device and a method of fabricating the same.
2. Description of the Related Art
Recently, with the increased degree of integration of semiconductor devices and rising demand for high performance thereof, metal interconnection of the semiconductor devices employs a multi-layer metal interconnection structure. In particular, the semiconductor memory devices, for example graphic dynamic random access memory (DRAM) devices requiring high speed operation exhibit a trend toward use of a tri layer metal interconnection structure instead of a double layer metal interconnection structure in metal interconnection. In order to reduce the RC signal delay caused by resistance components of metal interconnection layers and capacitor components of intermetallic dielectric layers in such multi-layer metal interconnection structures, the metal interconnection layers should be formed of metal materials having low specific resistance, and further, the intermetallic dielectric layers should be formed of materials having a low dielectric constant. In compliance with such requirements, recently, there is a trend toward formation of the intermetallic dielectric layers using low-k materials having a low dielectric constant.
Meanwhile, in order to reduce sheet resistance (Rs) of the metal interconnection layer itself, the thickness thereof should be increased. However, as the thickness of the metal interconnection layer increases, the thickness of the intermetallic dielectric layer should also be increased. On the other hand, in the case of low-k Spin On Glass (SOG)-based dielectric layers, which have recently been used as the intermetallic dielectric layer, the stress applied to the lower metal interconnection layer is increased when the thickness of the intermetallic dielectric layer is thicker than a certain thickness, and such stress is localized in specific regions, for example end parts of the metal interconnection layer, which correspond to edge parts of a wafer, upon heat treatment of the metal interconnection layer, causing cracks or lifting of the lower metal interconnection layers.
In order to solve such problems, silicon dioxide (SiO2)-based materials having a low carbon content, as a buffer layer, have been conventionally disposed between the metal interconnection layer and intermetallic dielectric layer. As the silicon dioxide (SiO2)-based materials, mention may be made of LP-tetra-ethyl-ortho-silicate (LP-TEOS) oxide layers, Middle Temperature Oxide (MTO) layers and Low Temperature Oxide (LTO) layers, which are deposited via use of Low Pressure Chemical Vapor Deposition (LPCVD), for example. Formation of such silicon dioxide (SiO2)-based materials involves a high-temperature process of more than 600° C. Therefore, when aluminum (Al) or the like is employed as the lower metal interconnection layers, such a high-temperature process adversely affects the lower metal interconnection layers including aluminum (Al), thus making it difficult to enter practical application thereof. In contrast, where Plasma Enhanced Oxide (PEOX) involving a relatively low-temperature process is employed, plasma induced damage results in poor properties of transistors in cell regions and peripheral circuit regions, thus making it even more difficult to enter practical application thereof. Further, such a Plasma Enhanced Oxide exhibits relatively low stress-relieving properties and therefore cannot sufficiently serve as the buffer layer.